The present invention is directed to a method, apparatus and system for call forwarding when roaming from a first type network to a second type network in a communication system. More specifically, the present invention relates in general to cellular communication systems and in particular to a method and apparatus for completing call forwarding when a dial mode ANSI-41 mobile subscriber has roamed to a GSM network and a call to that mobile subscriber is not terminated.
Cellular telephones have become increasingly prevalent in today""s society. The cellular telephone makes use of a cellular network and traditional telephone networks to route calls using radio communication signals. Two types of cellular networks have evolvedxe2x80x94Global Systems for Mobile communications (GSM) and American National Standards Institute-41 (ANSI-41) type networks. ANSI-41 is also sometimes referred to as IS 41 (TIA/EIA [Telecommunications Industry Association/Electronic Industries Association] Interim Standard 41).
The two types of cellular networks use message formats that are not completely compatible with one another as they are. Thus, if a mobile subscriber (MS) using cellular communication, roams from one type of network to another, the messages sent by the MS may not be understood by the network into which it roams unless some sort of conversion is performed. In order to allow roaming between xe2x80x9cforeignxe2x80x9d type networks, a signaling message converter, referred to herein as an IWU (InterWorking/interoperability Unit) operates to interconnect calling and called Mobile services Switching Centers (MSCs). The IWU passes signaling messages back and forth between network entities while converting the format of these messages such that the messages can be properly interpreted by the receiving MSC.
However, even with known signal message converters, GSM standards are inherently different from the ANSI-41 standards mentioned above. One of these differences is in the operation of xe2x80x9clate call forwardingxe2x80x9d or the action of the system when a call to a mobile subscriber (MS) cannot be terminated, i.e. connection completed, for any of several specific reasons like call collision, no page response of a page request sent to the called MS, and the like. A GSM system expects the terminating Mobile service Switching Center (MSC) to handle the call forwarding while an ANSI-41 system expects the originating or home MSC of the MS to handle the call forwarding.
As is known by those skilled in the art, call forwarding may occur when a call, to a given MS, cannot be terminated. The call forwarding can be xe2x80x9cearlyxe2x80x9d or xe2x80x9clatexe2x80x9d. Early call forwarding is defined as occurring when a contact with the MS has failed due to predetermined circumstances occurring while attempting to extend the call to another network. Late call forwarding is defined as occurring when call forwarding is initiated after the call has been extended to the last known xe2x80x9cforeignxe2x80x9d public land mobile network location and contact with the MS has failed due to predetermined circumstances.
In view of the above, it would be advantageous to have a converter mechanism that provides for late call forwarding from the originating MSC when a MS roams from an ANSI-41 network to a GSM network.
The present invention provides an apparatus, system and method for call forwarding when roaming from a first type network to a second type network.
According to one embodiment of the present invention, a signaling message converter signals an appropriate MSC in a local communication system to redirect a call when a terminating foreign MSC cannot terminate the call due to various circumstances. In a preferred embodiment, the calling party is located in a local communication system while the called party is in a foreign communication system. Once it is determined that the call cannot be terminated at the called party""s communication device in the foreign communication system, a call redirect message is sent to an appropriate MSC of the local communication system. In response to receiving the call redirect message, a call forwarding number is identified. The communication connection between the local communication system and the foreign communication system is released and a communication connection to the communication device associated with the call forwarding number is thereafter attempted.
Thus, with the present invention, call forwarding from an originating MSC can be accomplished when the called party is located in a foreign communication system. Other features and advantages of the present invention will be described in, or will become apparent to those of ordinary skill in the art in view of, the following detailed description of the preferred embodiment.